Here are some more details from Ars Tecnica, which should clarify Microsoft and NSS Labs “sponsorship” deal.

In terms of sponsorship of the reports, “this stuff is expensive to do right, and we need to monetize it somehow,” Moy told Ars. “We invited Google, Mozilla, Apple, Opera to participate, but they didn’t even bother to respond, except for Opera, which stated they “don’t really focus on malware.”

Also, readers have noticed that Firefox 3.5 was not included in those tests, here is a reason (as from .pdf).

We would have liked to have been able to test Firefox 3.5 which was released on June 30, 2009, and attempted to test it alongside the other browsers. However, serious instability where the browser repeatedly crashed (a widely reported issue) along with poor results prevented its inclusion for the sake of fairness.

Microsoft might be closer to a compromise with browser rival regarding Internet Explorer on Windows, but access to key online services for PCs could be the next hurdle.

Opera Software chief executive told The Reg he welcomed Microsoft’s offer last month to give European PC users a choice of browsers on Windows, but he warned of “problems” if rival browsers don’t get equal access to crucial sites that help keep users’ PCs secure and updated.